Infrared vidicon with off-axis electron gun

ABSTRACT

An infrared camera tube uses an electron beam to scan its photoconductive sensitive surface and produce an output. In order to avoid background current which might be produced by the thermonic cathode of the tube, the cathode is located off-axis of the tube. Magnets are used to deflect the electron beam first toward and then parallel to the tube axis. The beam is then focused and deflected in the usual manner.

United States Patent Miller [75] Inrentor: LOUIS D. Miller, Leola, Pa. ..lmaging Tube Detectors" by Rose published in, [73] Assignee: The United States of America as SPACE/AERONAUTICS, Nov. 1961, pp. 1 l31 16.

represented by the Secretary of the Army, Washmgton, Primary ExaminerHarold A. Dixon [22] Filed: 1, 1973 Attorney, Agent, or Firm-Lawrence A. Neureither;

Joseph H. Beumer; Aubrey J. Dunn [21] Appl. No.: 411,611

- [57] ABSTRACT {ill 11.1 .81.1::31I:1:1:f????.?913 T233512 An iefeeeee e eleeeeee eeem ee [58] Field of Search"... 250/338 213 VT 332, 334, scan its photoconductlve sens1 t1ve surface and pro 250/333 duce an output. In order to avold background current which might be produced by the thermonic cathode of he tube the cathode is located off-axis of the tube. [56] References Cited 1 e e Magnets are used to deflect the electron beam first to- UNITED STATES PATENTS ward and then parallel to the tube axis. The beam is 2,288,766 7/1942 wOlff 250/332 then focused and deflected in the usual manner 2,999,177 9/1961 Null et a] .1 250/338 3,040,177 6/1962 Rudnick et a1. 250/213 VT 4 Claims, 2 Drawing Figures 1 El 19 I j 10 51ml l 12 E m r 1 e 20 17 21 1 OUTPUT INFRARED VIDICON WITH OFF-AXIS ELECTRON GUN 3,596,097 7/1971 Robillard 250/338 OTHER PUBLICATIONS INFRARED VIDICON WITH OFF-AXIS ELECTRON GUN BACKGROUND OF THE INVENTION New York, 1963. This book bears Library of Congress Catalog Card Number: 62-8776. The instant invention is a vidicon of more conventional construction that shown by Krause et al. Other solutions are those shown in US. Pat. Nos. 2,928,971, 2,947,896 and 3,014,148, respectively issued Mar. 15, 1960, Aug. 2, 1960 and Dec. 19, 1961.

SUMMARY OF THE INVENTION The invention is an infrared vidicon having an electron gun offset from the longitudinal axis of the vidicon. Magnets are employed to bend the electron beam toward, then coaxial with the longitudinal axis. The infrared photoconductive sensitive surface of the vidicon is thus shielded from infrared energy emitted by the thermonic cathode of the electron gun.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a schematic side section of the invention.

FIG. 2 shows a sectional end view of the invention, taken in the direction as indicated in 22 in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION The invention may be best understood by reference to the drawings. FIG. 1 shows a schematic side view of the invention in which 10 designates the glass envelope, with connecting pins 11 and infrared photoconductive sensitive surface 12. The electron gun includes cathode 13 with heater 14, and elements G G and As can be seen, the cathode and heater and G and G are offaxis from envelope 10. Element 6;, is perforated at 15 and 16 for entry and exit of the electron beam. The path of the electron beam is shown by dotted lines and is first bend toward the longitudinal axis of by magnet 17, and then parallel to this axis by magnet 18. Each of 17 and 18 have pairs of pole pieces 19. As can be seen more clearly in FIG. 2, magnets 17 and 18 are electromagnets with windings connected to a D-C source (not shown). Although the connections are not shown in the drawings, elements G G and G would be connected to respective ones of pins 11. The usual alignment coil 20 and deflection and focusing coil 21 are shown and have their usual connections (not shown). Also shown is the system whereby an output is taken: i.e., D-C power source B and load resistor R,

connected between cathode l3 and sensitive surface While a specific embodiment of the invention has been shown and described, other embodiments within the scope of the invention may be obvious to ones skilled in the art. For example, magnets 17 and 18 may be permanent magnets, adjustable in position. The magnetism of electromagnets l7 and 18 may be adjusted to properly deflect the-electron beam by varying the current through the coils of 17 and 18.

The cathode of the inventive vidicon is therefore not visible from sensitive surface 12, but the electron beam from the cathode can reach 12. It may be necessary to blacken in interior of G in order to avoid the reflection of energy from 13 toward 12. Although not heretofore mentioned, 12 may be cooled in the usual manner, as shown in the book memtioned above in the Background of the Invention.

I claim:

1. An infrared vidicon having an elongated sealed envelope with a central longitudinal axis and with an electron gun in one end and an infrared sensitive surface in the other end, and electron beam deflection means:

said electron gun including athermonic cathode, at

least one control grid, and having a longitudinal axis parallel to but offset from the longitudinal axis of said envelope,

' said vidicon further including electron beam bending means including means for deflecting the beam from said gun first toward and then coaxial with the longitudinal axis of said envelope.

2. The vidicon as defined in claim 1 wherein said electron beam bending means includes a pair of magnets.

3. The vidicon as defined in claim 2 wherein said magnets are electromagnets.

4. The vidicon as defined in claim 3 where the final beam forming member of said electron gun has an offaxis perforation and an axial perforation. 

1. An infrared vidicon having an elongated sealed envelope with a central longitudinal axis and with an electron gun in one end and an infrared sensitive surface in the other end, and electron beam deflection means: said electron gun including a thermonic cathode, at least one control grid, and having a longitudinal axis parallel to but offset from the longitudinal axis of said envelope, said vidicon further including electron beam bending means including means for deflecting the beam from said gun first toward and then coaxial with the longitudinal axis of said envelope.
 2. The vidicon as defined in claim 1 wherein said electron beam bending means includes a pair of magnets.
 3. The vidicon as defined in claim 2 wherein said magnets are electromagnets.
 4. The vidicon as defined in claim 3 where the final beam forming member of said electron gun has an off-axis perforation and an axial perforation. 